<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS Arrow</title>
    <style>
        .arrow {
            content: '';
            border-top: 10px solid transparent;
            border-bottom: 10px solid transparent;
            border-left: 20px solid black;
            transform: rotate(0deg); /* 您可以调整旋转角度以改变箭头的方向 */
        }
    </style>
</head>
<body>
<div class="arrow"></div>
</body>
</html>